Oopse!!

So, what happened was my boyfriend and I were having sex and the condom broke. And a small about of semen got inside of me. However, I wasn't particularly worried. If you take into consideration that my boyfriend has a lower sperm count than most men. Even if we were activley trying the chances of me getting pregnant would be 50/50. Not only that, but I thought my period was over, but after it was over when I went to the bathroom I was bleeding still. My boyfriend, bless his soul, was still worried and bought me Take Action, a Plan B pill. Which I took the next morning. I feel pretty confident I'm not going to get pregnant, but I am aware that the body is a pretty funny thing. What do you think? Am I good to go? Or should I still be worried?